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OpenGL objects on terrain

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hi, i have created a terrain using c and opengl. now i wish to place some objects like a tree or cattle on the terrain. how do i do it? can it be done using opengl??

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glBegin(GL_TRIANGLES);
drawCastle();
glEnd();


Okay, seriously. If you ask an open-ended question like this, you have to expect some pretty open-ended answers.

So. I'd suggest you make a castle or tree in a 3D modeller, like Blender or Milkshape 3D, both freeware and with either very simple file formats or very easy to make custom exporters for. In fact, Blender has a 3DS exporter, and I'm sure there's a half-dozen free 3DS readers out there which produce a model object with built-in OpenGL drawing routines.

Alternatively, you can just draw your castle using hard-coded GL primitives. You know, yourself, what a castle looks like. So make a drawWall() method that draws a wall from (0,0,0) to (1,0,0) and tile or rotate a few of those to make the walls. Make a drawTower() method that draws a tower from (0,0,0) to (0,0,1), and scale a few of those to the size you want. I suggest using a display list or vertex buffer, storing your entire castle into it, and then drawing it with a single batched call later on (after you get your slow prototype working, of course).

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sorry for my query being insufficient..

i have a glb model of the object (cattle/man/woman)and a terrain.
what i wanted to know is how do i make model appear on the terrain.

any suggestions..

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Quote:
Original post by Hodgman
Which part are you having problems with - loading the glb model, rendering the loaded model, or positioning the model at the correct place in the world?


actually i havent yet started with any of these..so i need help regarding all the parts..

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instead of the model i would like to place an image eg. tree.jpg/tree.bmp on the terrain.
can anyone tell me how this can be done.
or else suggest me some site/tutorial for the same.

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Look up billboards and impostors.

I'm not familiar with GLB files, but you could always try wotsit, a huge repository of information about open and proprietary file formats: http://www.wotsit.org/

As far as getting around to the rendering, if you're drawing a terrain you've honestly already got 3/4s of what you need to know to draw the trees and other objects on it down pat.

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hi

thats exactly what i want to know. how do i render the tree which is an image jpg/bmp on to the terrain..

first i load the image from the file,
then how do i render it??

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Quote:
Original post by vpk
Quote:
Original post by Wyrframe
Quote:
Original post by vpk
i would like to place an image eg. tree.jpg/tree.bmp on the terrain.
Look up billboards and impostors.
how do i render the tree which is an image jpg/bmp on to the terrain..
Billboards @ Flipcode.
Billboards @ NeHe.

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i have gone thru the sites..

i dont want to rotate the tree , i just want to place it on the terrain after loading it..

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I don't know much about opengl, but logic dictates that if you can render a terrain - you can render other objects like a tree. Export a textured quad that looks like a tree, possibly with some alpha blending - then render it in the same way you rendered your terrain.

The rotation is neccessary if you want the tree to always face the camera to trick the viewer into thinking it's 3d - i.e. billboarding.

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i understand what u are saying, but..

see i have a tga file with the image of a tree, now i want to render it on the terrain. i know i have to first load the file and then render it..

but i am not able to do it..

can anyone suggest a simple code for doing the same??

with anticipation
regards

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Does the word "texture" mean something for you ? If no you should start to learn it first, and how to use it (cf. nehe tutorial about texture in OpenGL). Then your problem is solved: drawing trees as billboards is just drawing a quad and applying your tree texture on it.

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i know you all are experts in the domain on this forum, but please understand that i am just a beginner..so sorry if u feel i am asking nonsensical questions.

i have the image of a tree do i still have to draw a quad??

can u please post a simple code wherein i load the file,render it to the terrain??

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Create a quad with the texture of the tree. This will allow you to draw the tree as a quad.

Now, there are two problems here:

First, the quad is flat, so if you look at it sideways, the 3D illusion will be ruined. To fix this, you have to make sure that the quad always faces the camera, and this will make it look like a 3D tree (well sort of). This is called billboarding and is covered in the articles linked earlier.

Second, you need the tree to be placed on the terrain. You can decide on the tree's x and z position, but the y position will be determined by the height of the terrain at that coordinate, so the tree's world position would be:

(x, terrainHeightAt(x, z), z)

So given an (x, z) pair, you need to know the terrain's height at that location. You can find a good explanation of that here.

If this doesn't answer your question, you'll need to be more specific.

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i understand i have to create a quad for the tree, but how do i do it??

in case of terrain i had the height values which i used to display the heightmap..
but in case of tree i have a image file, how do i do the tree??

pleaseee give me an example..

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I don't use OpenGL so I don't know it well enough to write the code, but there are some video tutorials here that you might want to go over. Look at their outline to see what's covered (you'll probably find tutorial 11 especially interesting).

Of course, doing a google search will turn up many more tutorials.

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If you've drawn the terrain already, you either know how to create quads and/or triangles, or else you've just copy/pasted some source and don't understand it.

Read the tutorials linked-to above; you'll see both the why and the how explained in them.

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Quote:
Original post by Wyrframe
If you've drawn the terrain already, you either know how to create quads and/or triangles, or else you've just copy/pasted some source and don't understand it.



are you angry with me for asking questions?? i have no experience in this hence i am asking you questions..

ok, i have gone thru some of the links but what i understand is that they tell how to texture the whole object after reading a single bmp file.

thats fine, i understood.

but whats happening with me is that the terrain has one texture and i am trying to put a tree with another texture.there are 2 files. when i read and load the texture, the texture of the terrain gets changed and the tree is not displayed.


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Quote:
Original post by vpk
whats happening with me is that the terrain has one texture and i am trying to put a tree with another texture.there are 2 files. when i read and load the texture, the texture of the terrain gets changed and the tree is not displayed.


You need to set the texture for each object before drawing it, so your code should look something like this:


setTexture(terrainTexture);
drawTerrain();
setTexture(treeTexture);
drawQuad();

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If you read nehe tuttorial about texture the you know how to load a file and associate it with a unique texture Id. Then you just have to switch from one texture to another before drawing your objects, like Gage64 said.

BTW drawing a quad in OpenGL is something like this:

glMatrixMode (GL_MODELVIEW);
glPushMatrix();
glTranslatef(quadPosition[0],quadPosition[1],quadPosition[2]);
glRotatef(...); // calculate some angles to make it face the camera
glBegin(GL_QUADS);
glTexCoord2f(0.0,0.0);
glVertex3f(0.0,0.0,0.0);

glTexCoord2f(1.0,0.0);
glVertex3f(width,0.0,0.0);

glTexCoord2f(1.0,1.0);
glVertex3f(width,height,0.0);

glTexCoord2f(0.0,1.0);
glVertex3f(0.0,height,0.0);
glEnd();
glPopMatrix();

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i tried doing the same . but the tree appears as a flat texture on the terrain
ie. it should be vertically placed but it gets covered horizontally.

can u give some sample code for the same which is easy to follow, please..

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void TreeRender()
{
glMatrixMode(GL_MODELVIEW);
int Height;
unsigned char * data1;
FILE * file;

//for texture
file = fopen("tree1.bmp", "rb" );
data1 = (unsigned char *)malloc( 256 * 256 * 3 );
fread( data1, 256 * 256 * 3, 1, file );
fclose( file );

glGenTextures( 1, &texture1 ); //generate the texture with the loaded data
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, texture1);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT );
glTexParameterf( GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT );

//Generate the texture with mipmaps
gluBuild2DMipmaps( GL_TEXTURE_2D, 3, 256, 256, GL_RGB, GL_UNSIGNED_BYTE, data1 );
free( data1 );
//till here

//for display
treeList.m_position[0]=absCameraPos.x+1.0;
treeList.m_position[1]=GetY(absCameraPos.x,absCameraPos.z);
treeList.m_position[2]=absCameraPos.z+1.0;
glPushMatrix();
glTranslatef(treeList.m_position[0],treeList.m_position[1],treeList.m_position[2]);
glBegin(GL_QUADS);
glTexCoord2f(0.0,0.0);
glVertex3f(0.0,0.0,0.0);

glTexCoord2f(1.0,0.0);
glVertex3f(1.0,0.0,0.0);

glTexCoord2f(1.0,1.0);
glVertex3f(1.0,1.0,0.0);

glTexCoord2f(0.0,1.0);
glVertex3f(0.0,1.0,0.0);
glEnd();

glDisable(GL_TEXTURE_2D);
//till here

}


please tell me where i am going wrong??

i am loading the texture for terrain,drawing the terrain then loading texture for tree and then rendering it..

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Loading and creating texture should be done only once so you'd better move corresponding instructions in an init() function which you call once at the beginning of your program. Then in the main loop you can call your drawing functions. In my example, the coordinates system may differs from your: I use y-axis as the vertical axis this may be why it looks flat in your program. BTW you can use the glRotatef(..) function to make it stand up.

Also don't forget the glPopMatrix(); after drawing the tree.

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Quote:
Original post by Shirakana2
Loading and creating texture should be done only once so you'd better move corresponding instructions in an init() function which you call once at the beginning of your program. Then in the main loop you can call your drawing functions.


yes, i have done that and now my terrain has its initial texture.thank you

In my example, the coordinates system may differs from your: I use y-axis as the vertical axis this may be why it looks flat in your program. BTW you can use the glRotatef(..) function to make it stand up.

Also don't forget the glPopMatrix(); after drawing the tree.[/quote]

but the tree rendering still has some problem. i am not clear what coordinates do i give in the GL_QUADS. should i specify the terrain vertices??


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      When sampling a texture in a shader, the texture sampler was traditionally specified as separate object that was bound to the pipeline at run time or set as part of the texture object itself. However, in most cases it is known beforehand what kind of sampler will be used in the shader. Next-generation APIs expose new type of sampler called static sampler that can be initialized directly in the pipeline state. Diligent Engine exposes this functionality: when creating a shader, textures can be assigned static samplers. If static sampler is assigned, it will always be used instead of the one initialized in the texture shader resource view. To initialize static samplers, prepare an array of StaticSamplerDesc structures and initialize StaticSamplers and NumStaticSamplers members. Static samplers are more efficient and it is highly recommended to use them whenever possible. On older APIs, static samplers are emulated via generic sampler objects.
      The following is an example of shader initialization:
      ShaderCreationAttribs Attrs; Attrs.Desc.Name = "MyPixelShader"; Attrs.FilePath = "MyShaderFile.fx"; Attrs.SearchDirectories = "shaders;shaders\\inc;"; Attrs.EntryPoint = "MyPixelShader"; Attrs.Desc.ShaderType = SHADER_TYPE_PIXEL; Attrs.SourceLanguage = SHADER_SOURCE_LANGUAGE_HLSL; BasicShaderSourceStreamFactory BasicSSSFactory(Attrs.SearchDirectories); Attrs.pShaderSourceStreamFactory = &BasicSSSFactory; ShaderVariableDesc ShaderVars[] = {     {"g_StaticTexture", SHADER_VARIABLE_TYPE_STATIC},     {"g_MutableTexture", SHADER_VARIABLE_TYPE_MUTABLE},     {"g_DynamicTexture", SHADER_VARIABLE_TYPE_DYNAMIC} }; Attrs.Desc.VariableDesc = ShaderVars; Attrs.Desc.NumVariables = _countof(ShaderVars); Attrs.Desc.DefaultVariableType = SHADER_VARIABLE_TYPE_STATIC; StaticSamplerDesc StaticSampler; StaticSampler.Desc.MinFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MagFilter = FILTER_TYPE_LINEAR; StaticSampler.Desc.MipFilter = FILTER_TYPE_LINEAR; StaticSampler.TextureName = "g_MutableTexture"; Attrs.Desc.NumStaticSamplers = 1; Attrs.Desc.StaticSamplers = &StaticSampler; ShaderMacroHelper Macros; Macros.AddShaderMacro("USE_SHADOWS", 1); Macros.AddShaderMacro("NUM_SHADOW_SAMPLES", 4); Macros.Finalize(); Attrs.Macros = Macros; RefCntAutoPtr<IShader> pShader; m_pDevice->CreateShader( Attrs, &pShader );
      Creating the Pipeline State Object
      After all required shaders are created, the rest of the fields of the PipelineStateDesc structure provide depth-stencil, rasterizer, and blend state descriptions, the number and format of render targets, input layout format, etc. For instance, rasterizer state can be described as follows:
      PipelineStateDesc PSODesc; RasterizerStateDesc &RasterizerDesc = PSODesc.GraphicsPipeline.RasterizerDesc; RasterizerDesc.FillMode = FILL_MODE_SOLID; RasterizerDesc.CullMode = CULL_MODE_NONE; RasterizerDesc.FrontCounterClockwise = True; RasterizerDesc.ScissorEnable = True; RasterizerDesc.AntialiasedLineEnable = False; Depth-stencil and blend states are defined in a similar fashion.
      Another important thing that pipeline state object encompasses is the input layout description that defines how inputs to the vertex shader, which is the very first shader stage, should be read from the memory. Input layout may define several vertex streams that contain values of different formats and sizes:
      // Define input layout InputLayoutDesc &Layout = PSODesc.GraphicsPipeline.InputLayout; LayoutElement TextLayoutElems[] = {     LayoutElement( 0, 0, 3, VT_FLOAT32, False ),     LayoutElement( 1, 0, 4, VT_UINT8, True ),     LayoutElement( 2, 0, 2, VT_FLOAT32, False ), }; Layout.LayoutElements = TextLayoutElems; Layout.NumElements = _countof( TextLayoutElems ); Finally, pipeline state defines primitive topology type. When all required members are initialized, a pipeline state object can be created by IRenderDevice::CreatePipelineState() method:
      // Define shader and primitive topology PSODesc.GraphicsPipeline.PrimitiveTopologyType = PRIMITIVE_TOPOLOGY_TYPE_TRIANGLE; PSODesc.GraphicsPipeline.pVS = pVertexShader; PSODesc.GraphicsPipeline.pPS = pPixelShader; PSODesc.Name = "My pipeline state"; m_pDev->CreatePipelineState(PSODesc, &m_pPSO); When PSO object is bound to the pipeline, the engine invokes all API-specific commands to set all states specified by the object. In case of Direct3D12 this maps directly to setting the D3D12 PSO object. In case of Direct3D11, this involves setting individual state objects (such as rasterizer and blend states), shaders, input layout etc. In case of OpenGL, this requires a number of fine-grain state tweaking calls. Diligent Engine keeps track of currently bound states and only calls functions to update these states that have actually changed.
      Binding Shader Resources
      Direct3D11 and OpenGL utilize fine-grain resource binding models, where an application binds individual buffers and textures to certain shader or program resource binding slots. Direct3D12 uses a very different approach, where resource descriptors are grouped into tables, and an application can bind all resources in the table at once by setting the table in the command list. Resource binding model in Diligent Engine is designed to leverage this new method. It introduces a new object called shader resource binding that encapsulates all resource bindings required for all shaders in a certain pipeline state. It also introduces the classification of shader variables based on the frequency of expected change that helps the engine group them into tables under the hood:
      Static variables (SHADER_VARIABLE_TYPE_STATIC) are variables that are expected to be set only once. They may not be changed once a resource is bound to the variable. Such variables are intended to hold global constants such as camera attributes or global light attributes constant buffers. Mutable variables (SHADER_VARIABLE_TYPE_MUTABLE) define resources that are expected to change on a per-material frequency. Examples may include diffuse textures, normal maps etc. Dynamic variables (SHADER_VARIABLE_TYPE_DYNAMIC) are expected to change frequently and randomly. Shader variable type must be specified during shader creation by populating an array of ShaderVariableDesc structures and initializing ShaderCreationAttribs::Desc::VariableDesc and ShaderCreationAttribs::Desc::NumVariables members (see example of shader creation above).
      Static variables cannot be changed once a resource is bound to the variable. They are bound directly to the shader object. For instance, a shadow map texture is not expected to change after it is created, so it can be bound directly to the shader:
      PixelShader->GetShaderVariable( "g_tex2DShadowMap" )->Set( pShadowMapSRV ); Mutable and dynamic variables are bound via a new Shader Resource Binding object (SRB) that is created by the pipeline state (IPipelineState::CreateShaderResourceBinding()):
      m_pPSO->CreateShaderResourceBinding(&m_pSRB); Note that an SRB is only compatible with the pipeline state it was created from. SRB object inherits all static bindings from shaders in the pipeline, but is not allowed to change them.
      Mutable resources can only be set once for every instance of a shader resource binding. Such resources are intended to define specific material properties. For instance, a diffuse texture for a specific material is not expected to change once the material is defined and can be set right after the SRB object has been created:
      m_pSRB->GetVariable(SHADER_TYPE_PIXEL, "tex2DDiffuse")->Set(pDiffuseTexSRV); In some cases it is necessary to bind a new resource to a variable every time a draw command is invoked. Such variables should be labeled as dynamic, which will allow setting them multiple times through the same SRB object:
      m_pSRB->GetVariable(SHADER_TYPE_VERTEX, "cbRandomAttribs")->Set(pRandomAttrsCB); Under the hood, the engine pre-allocates descriptor tables for static and mutable resources when an SRB objcet is created. Space for dynamic resources is dynamically allocated at run time. Static and mutable resources are thus more efficient and should be used whenever possible.
      As you can see, Diligent Engine does not expose low-level details of how resources are bound to shader variables. One reason for this is that these details are very different for various APIs. The other reason is that using low-level binding methods is extremely error-prone: it is very easy to forget to bind some resource, or bind incorrect resource such as bind a buffer to the variable that is in fact a texture, especially during shader development when everything changes fast. Diligent Engine instead relies on shader reflection system to automatically query the list of all shader variables. Grouping variables based on three types mentioned above allows the engine to create optimized layout and take heavy lifting of matching resources to API-specific resource location, register or descriptor in the table.
      This post gives more details about the resource binding model in Diligent Engine.
      Setting the Pipeline State and Committing Shader Resources
      Before any draw or compute command can be invoked, the pipeline state needs to be bound to the context:
      m_pContext->SetPipelineState(m_pPSO); Under the hood, the engine sets the internal PSO object in the command list or calls all the required native API functions to properly configure all pipeline stages.
      The next step is to bind all required shader resources to the GPU pipeline, which is accomplished by IDeviceContext::CommitShaderResources() method:
      m_pContext->CommitShaderResources(m_pSRB, COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES); The method takes a pointer to the shader resource binding object and makes all resources the object holds available for the shaders. In the case of D3D12, this only requires setting appropriate descriptor tables in the command list. For older APIs, this typically requires setting all resources individually.
      Next-generation APIs require the application to track the state of every resource and explicitly inform the system about all state transitions. For instance, if a texture was used as render target before, while the next draw command is going to use it as shader resource, a transition barrier needs to be executed. Diligent Engine does the heavy lifting of state tracking.  When CommitShaderResources() method is called with COMMIT_SHADER_RESOURCES_FLAG_TRANSITION_RESOURCES flag, the engine commits and transitions resources to correct states at the same time. Note that transitioning resources does introduce some overhead. The engine tracks state of every resource and it will not issue the barrier if the state is already correct. But checking resource state is an overhead that can sometimes be avoided. The engine provides IDeviceContext::TransitionShaderResources() method that only transitions resources:
      m_pContext->TransitionShaderResources(m_pPSO, m_pSRB); In some scenarios it is more efficient to transition resources once and then only commit them.
      Invoking Draw Command
      The final step is to set states that are not part of the PSO, such as render targets, vertex and index buffers. Diligent Engine uses Direct3D11-syle API that is translated to other native API calls under the hood:
      ITextureView *pRTVs[] = {m_pRTV}; m_pContext->SetRenderTargets(_countof( pRTVs ), pRTVs, m_pDSV); // Clear render target and depth buffer const float zero[4] = {0, 0, 0, 0}; m_pContext->ClearRenderTarget(nullptr, zero); m_pContext->ClearDepthStencil(nullptr, CLEAR_DEPTH_FLAG, 1.f); // Set vertex and index buffers IBuffer *buffer[] = {m_pVertexBuffer}; Uint32 offsets[] = {0}; Uint32 strides[] = {sizeof(MyVertex)}; m_pContext->SetVertexBuffers(0, 1, buffer, strides, offsets, SET_VERTEX_BUFFERS_FLAG_RESET); m_pContext->SetIndexBuffer(m_pIndexBuffer, 0); Different native APIs use various set of function to execute draw commands depending on command details (if the command is indexed, instanced or both, what offsets in the source buffers are used etc.). For instance, there are 5 draw commands in Direct3D11 and more than 9 commands in OpenGL with something like glDrawElementsInstancedBaseVertexBaseInstance not uncommon. Diligent Engine hides all details with single IDeviceContext::Draw() method that takes takes DrawAttribs structure as an argument. The structure members define all attributes required to perform the command (primitive topology, number of vertices or indices, if draw call is indexed or not, if draw call is instanced or not, if draw call is indirect or not, etc.). For example:
      DrawAttribs attrs; attrs.IsIndexed = true; attrs.IndexType = VT_UINT16; attrs.NumIndices = 36; attrs.Topology = PRIMITIVE_TOPOLOGY_TRIANGLE_LIST; pContext->Draw(attrs); For compute commands, there is IDeviceContext::DispatchCompute() method that takes DispatchComputeAttribs structure that defines compute grid dimension.
      Source Code
      Full engine source code is available on GitHub and is free to use. The repository contains tutorials, sample applications, asteroids performance benchmark and an example Unity project that uses Diligent Engine in native plugin.
      Atmospheric scattering sample demonstrates how Diligent Engine can be used to implement various rendering tasks: loading textures from files, using complex shaders, rendering to multiple render targets, using compute shaders and unordered access views, etc.

      Asteroids performance benchmark is based on this demo developed by Intel. It renders 50,000 unique textured asteroids and allows comparing performance of Direct3D11 and Direct3D12 implementations. Every asteroid is a combination of one of 1000 unique meshes and one of 10 unique textures.

      Finally, there is an example project that shows how Diligent Engine can be integrated with Unity.

      Future Work
      The engine is under active development. It currently supports Windows desktop, Universal Windows, Linux, Android, MacOS, and iOS platforms. Direct3D11, Direct3D12, OpenGL/GLES backends are now feature complete. Vulkan backend is coming next, and Metal backend is in the plan.
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